This invention relates to a process for the surface finishing of thermoplastic film or sheet when it is in the molten or softened state. This state could be attained by the use of an extruder, calender stack or some means of heating the film or sheet to its softening temperature. The method of this invention involves the pressing of a shape memory alloy endless belt into a thermoplastic film or sheet which has been heated above its softening temperature and then cooling the film or sheet and the belt through the belt's temperature transition range. The face of the shape memory alloy belt would have a desired finish on its face making contact with the film or sheet face.
In the production of thermoplastic film and sheet it is frequently desirable to use at least one roll with a relatively resilient surface in order to compensate for variations in the thickness of the film or sheet passing through the nip of two cooperating rolls, and to maintain a relatively uniform pressure across the width of the film or sheet. In many instances an endless belt, composed of metal or a resilient material, has been used in combination with the above mentioned rolls to transfer to the face of the film or sheet certain desirable characteristics. A few of these characteristics would be any one or combination of the following. The film or sheet could have a tendency to stick to the above mentioned cooperating rolls. The film or sheet could be mirror finished for clarity on one, or both, of its surfaces. The film or sheet could be embossed with a surface finish to hide imperfections. Or, the film or sheet could be embossed with a matte finish such that any of the following could be performed. The surface would be better suited for an adhesive coating or better suited for inking.
It is an object of the present invention to show that the use of an endless belt composed of a shape memory alloy is particularly useful in attaining the above. It is another object of this invention to show that if this belt has a coating of a resilient material such as silicone rubber applied to its embossing face, that this combination is also useful in attaining the above characteristics.